Disable DNSMasq DNS if port 53 conflict occurs

[DavidePrincipi]

The core Samba DC application and DNSMasq have a potential conflict on port 53. If port 53 is in use, DNSMasq UI displays a message and disable the DNS feature. However the port conflict may still arise if:

• DNSMasq is installed and configured from UI before Samba.
• During clone or restore of both modules, no matter the order they are re-configured by the core.

Proposed solution

DNSMasq can discover from Samba Redis keys and events if there is a conflicting DC on the local node and automatically disable its DNS feature.

Alternative solutions

A more general solution is viable, but would require much more effort. We can define an image label, like the existing org.nethserver.max-per-node, where the application lists the fixed ports it will use. The Core can identify potential port conflicts with installed apps in advance and deny the instance creation on every possible scenario: install, update, restore, clone.

Additional context

See also

Discussion https://mattermost.nethesis.it/nethesis/pl/9ko5xmf7oidijxkhku18xdtrzr

[DavidePrincipi]

In testing: 1.1.0-dev.2

Test case 1

• Install and configure dnsmasq, enable DNS feature
• Install Samba DC on another node: dnsmasq DNS is still enabled
• Install Samba DC on the same node of dnsmasq: DNS becomes disabled

Test case 2

• Restore dnsmasq from backup (with DNS enabled)
• Restore Samba DC from backup on the same node

Test case 3

• Install dnsmasq and configure DNS
• Install Samba DC on another node
• Move dnsmasq to the same node of Samba

Test case 4

Update a working dnsmasq instance to the testing version.

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In any case, port conflict on DNS port 53 must be handled by forcing DNS setting of DNSMasq to disabled.

[nrauso]

test case 1: VERIFIED
test case 2: VERIFIED
test case 3: VERIFIED
test case 4: VERIFIED

[DavidePrincipi]

Released https://github.com/NethServer/ns8-dnsmasq/releases/tag/1.1.0